1. Field of the Invention
The present invention relates to a wheel rim forming machine.
2. Description of the Related Art
On a conventional disk wheel manufacture line for manufacturing disk wheels for a vehicle, disk wheels are manufactured by the following series of steps. First, a long plate of predetermined width is cut to plates of a specified length and each cut plate is rolled by a coiler into a rolled plate. The circumferential ends of the rolled plate is butt welded together with a welding machine to form a cylindrical rim element. The cylindrical rim element is conveyed to a flaring machine where both axial end portions of the cylindrical rim element are flared. Then, the flared rim element is conveyed to a rim forming station provided with at least one rim forming machine where it is formed to produce a specified rim shape. The formed rim element is then conveyed to a shaping machine where it is shaped to define a final rim configuration. The shaped rim element is conveyed to a disk insertion station where a disk is inserted into the rim element. The rim element and the disk are then conveyed to a welding station where they are welded together to form a disk wheel. Finally, the disk wheel is painted.
The prior art wheel rim forming machine comprises a top roll and a bottom roll for squeezing the rim element wall therebetween and a pair of guide rolls for guiding the rim element during formation. The machine further comprises a frame including a fixed frame and a driven frame adapted to be driven vertically relative to the fixed frame. The fixed frame has a laterally extending "U"-shaped frame which has upper and lower horizontally extending legs and a vertically extending base portion which connects the two legs. The top roll and the pair of guide rolls are supported by the driven frame, whereas the bottom roll is supported by the fixed frame. More particularly, the top roll is supported by a top roll shaft inserted therethrough and supported, in turn, with bearing devices mounted at each end portion of the shaft and coupled to the vertically driven frame. The bottom roll and the support structure therefore are divided axially into two portions so that the bottom roll can be inserted through the rim element and supports the same from the inside.
Using this machine, the rim element is formed in the following way: When the rim element is conveyed to the forming position in the machine, the two portions of the bottom roll and the support structure therefore are moved to the interior of the rim element so as to support the rim element from the inside. Then, the top roll is driven downward toward the bottom roll and the rim element wall is squeezed between the top and bottom rolls. Then, the top roll is driven so as to rotate and the entire circumference of the rim element is formed to produce a specified rim shape. After forming, the top roll is raised, the two portions of the bottom roll and the support structure thereof are separated, and the formed rim element is ejected from the forming position to the next station. With this machine, when the shape or size of the rim element to be formed is changed, the top and bottom rolls and the pair of the guide rolls must also be changed so as to correspond to the desired shape, diameter, width and thickness of the rim element.
Furthermore, the rim forming machine described above has a number of shortcomings.
First, because the fixed frame is "U"-shaped with laterally extending legs, it tends to elastically deform, opening the "U" when the frame is exposed to an upwardly directed force from the top roll via the driven frame and a downwardly directed force from the bottom roll. Thus, the clearance between the top and bottom rolls can vary during rim element formation. This varies the diameter of the formed wheel rim which will undesirably increase the vertical vibration of an associated vehicle. In addition, the variation in clearance will vary the thickness of the rim and will decrease the strength of the wheel itself.
Second, because the fixed frame is a laterally extending U frame, the vertically extending portion of the U frame is designed to have a large cross section to increase its rigidity and hence decrease the likelihood of elastic deformation during rim formation. Accordingly, only a limited amount of space is left between the top roll and the vertically extending portion for providing one of the paired guide rolls and a supporting structure for the one guide roll which extends toward the vertically extending portion of the U frame. Therefore, access to and the adjustment of the one guide roll and the supporting structure are difficult when the guide roll is to be exchanged. Insufficient adjustment or low grade adjustment of the guide roll and the support structure thereof degrades the shape of the formed wheel rim in the width direction and this will cause a lateral vibration of the vehicle to which the wheel rim is mounted.